Hard disk drives are common information storage devices essentially consisting of a series of rotatable disks that are accessed by magnetic reading and writing elements. These data transferring elements, commonly known as transducers, are typically carried by and embedded in a slider body that is held in a close relative position over discrete data tracks formed on a disk to permit a read or write operation to be carried out. In order to properly position the transducer with respect to the disk surface, an air bearing surface (ABS) formed on the slider body experiences a fluid air flow that provides sufficient lift force to “fly” the slider and transducer above the disk data tracks. The high speed rotation of a magnetic disk generates a stream of air flow or wind along its surface in a direction substantially parallel to the tangential velocity of the disk. The air flow cooperates with the ABS of the slider body which enables the slider to fly above the spinning disk. In effect, the suspended slider is physically separated from the disk surface through this self-actuating air bearing. The ABS of a slider is generally configured on the slider surface facing the rotating disk, and greatly influences its ability to fly over the disk under various conditions.
As shown in FIG. 1 an ABS design known for a common catamaran slider 5 may be formed with a pair of parallel rails 2 and 4 that extend along the outer edges of the slider surface facing the disk. Other ABS configurations including three or more additional rails, with various surface areas and geometries, have also been developed. The two rails 2 and 4 typically run along at least a portion of the slider body length from the leading edge 6 to the trailing edge 8. The leading edge 6 is defined as the edge of the slider that the rotating disk passes before running the length of the slider 5 towards a trailing edge 8. As shown, the leading edge 6 may be tapered despite the large undesirable tolerance typically associated with this machining process. The transducer or magnetic element 7 is typically mounted at some location along the trailing edge 8 of the slider as shown in FIG. 1. The rails 2 and 4 form an air bearing surface on which the slider flies, and provide the necessary lift upon contact with the air flow created by the spinning disk. As the disk rotates, the generated wind or air flow runs along underneath, and in between, the catamaran slider rails 2 and 4. As the air flow passes beneath the rails 2 and 4, the air pressure between the rails and the disk increases thereby providing positive pressurization and lift. Catamaran sliders generally create a sufficient amount of lift, or positive load force, to cause the slider to fly at appropriate heights above the rotating disk. In the absence of the rails 2 and 4, the large surface area of the slider body 5 would produce an excessively large air bearing surface area In general, as the air bearing surface area increases, the amount of lift created is also increased.
As illustrated in FIG. 2, a head gimbal assembly 40 often provides the slider with multiple degrees of freedom such as vertical spacing, or pitch angle and roll angle which describe the flying height of the slider. As shown in FIG. 2, a suspension 74 holds the HGA 40 over the moving disk 76 (having edge 70) and moving in the direction indicated by arrow 80. In operation of the disk drive shown in FIG. 2, an actuator 72 moves the HGA over various diameters of the disk 76 (e.g., inner diameter (ID), middle diameter (MD) and outer diameter (OD)) over arc 78.
Giant Magnetoresistive (GMR) heads are being used more and more for advanced hard disk drives (e.g., capable of storing more than 80 gigabytes of data). GMR heads, which are well-known in the art, include components generally located in the middle of the trailing portion of the slider (not the air bearing surface of the slider). The GMR read sensor (for sensing data signals in the medium) tends to be susceptible to damage by electrostatic discharge (ESD). The write circuitry for the head typically includes an inductive coil (to create data signals in the medium) that are usually resilient against ESD damage.
The slider, as described above, is typically made of a ceramic such as Al2O3TiC, which is conductive. As the slider flies over the disk, the potential for the slider can be affected by triboelectric charge. Since the slider is conductive, this potential can be controlled by either grounding the slider or capacitive suppression (e.g., as described below).
Grounding of a slider may be accomplished, for example, by electrically coupling it to the conductive material of the slider suspension (e.g., stainless steel). On the other hand, if the connection between the slider substrate and the suspension is not sufficiently conductive, and the capacitance between them is appreciably larger than the capacitance of the slider-disk interface, then capacitive suppression is achieved.
In controlling the potential of the slider, grounding of the slider is more effective than capacitive suppression. In addition to coupling the slider, electrically, to the stainless steel suspension, the slider may also be provided with an extra conductive pad. In such a situation, a conductive trace would be provided on the suspension to connect the extra pad to ground.
Alternative to conductive sliders, a slider made of insulating material may be provided. For example, a slider made of alumina (Al2O3) may have superior mechanical properties (e.g., machining and reliability). However, a slider made only of insulating material poses serious ESD risks for the GMR sensor. First, when fabricating the sensor during wafer processes, the magnetic head cannot be discharged safely, which could damage the sensor. Second, during the manufacture of the head gimbal assembly (HGA), the slider substrate cannot be properly grounded. Third, debris in the slider to disk interface causes triboelectric charge (tribocharge) to build up. The resulting increased potential may exceed acceptable thresholds may damage the GMR head.
Therefore, insulating substrate has only been used with inductive recording heads, which are more resistant to ESD damage. U.S. Pat. No. 6,597,543 mentions an “insulating substrate” for MR read-heads. However the “insulating substrate” refers to a conventional Al2O3TiC substrate, which is a well-known conductor, covered by a thin layer of alumina, known as the “under-coat.” The application of this under-coat is also conventional practice. It simply insulates the GMR head from the conductive substrate. It does not render the Al2O3TiC substrate an insulating substance. U.S. Pat. Nos. 5,757,591 and 6,607,923 describe a sapphire wafer substrate which is truly insulating. A pair of build-in diodes is employed to reduce the risk of ESD damage. However, the diodes will not prevent ESD damage in case of dielectric breakdown (i.e., arcing) between the shield and the GMR stripe.
Referring to U.S. Pat. No. 6,453,542, shields are provided to protect the GMR head from ESD arcing. The shields are conductively connected to the GMR sensor. If the shields, however, receive a fast transient current (e.g., caused from passing debris at the slider to disk interface), the potential in the shield may be so large that arcing may occur between the shield and the sensor causing ESD damage.
In order to minimize fast transient current entering the shield, a prior-art solution is to ground the conductive slider substrate, so that passing debris can be discharged by the slider substrate as it approaches the shields. Obviously this solution is not applicable with an insulating slider substrate. In theory, a conductive coating may be applied to the slider substrate, to render the air-bearing surface (ABS) conductive. However to achieve high recording density, such a coating must be extremely thin (in the order of one nanometer). It is very difficult to achieve desired conductivity with such a thin coat. Furthermore, the coating will be subject to wear.
In view of the above, there is a need for an head/slider design that improves the protection for head/sensor damage due to ESD and the like.